1. Field of the Invention
The present invention is related to a sheet inverting apparatus, or to be more specific, an image forming apparatus equipped with an inverting roll to turn over the sheet on which the image is formed on the route of carrying the sheet.
2. Related Background Art
The conventional image forming apparatus is explained hereunder by taking a compact laser printer used for the output device of a data processing system as an example.
As illustrated in FIG. 1, a laser printer is provided with a process cartridge 3 which is removably attached to the main body 2 of the apparatus, the said process cartridge 3 accommodating the conventional processing apparatus such as photosensitive drum 4, electric charger 5, developing apparatus 6, cleaner 7 etc. At the upper part of the main body 2 of the apparatus is provided the scanner unit 8 and mirror 9 which irradiate a laser beam and execute scanning. A latent image corresponding to the specified image data is formed on the photosensitive drum 4 which is electrically charged by the charger 5 and the latent image is developed by the developing apparatus 6 to produce a toner image.
At the lower part of the main body 2 of the apparatus is arranged a sheet feeding cassette 10 which holds many sheets S, a sheet feeding roll 11 is arranged at the sheet feeding cassette 10, and the sheets S housed in the sheet feeding cassette 10 are delivered sheet by sheet to the regist or registration roller 12 by the sheet feeding roller 11. The said regist roller 12 adjusts the timing to deliver the sheet to the point in between the photosensitive drum 4 and transfer charger 13 and there the toner image on the photosensitive drum 4 is transferred. The sheet S on which toner image is transferred is delivered to the fixing apparatus 15 by conveyor belt unit 14, the toner image is fixed thereon and the sheet is discharged to outside of the main body 2 of the apparatus.
Laser printer 1 has two systems to discharge the sheet S, one being the system to discharge sheet S in face up posture i.e., the image plane facing upward, and discharge the sheet through the face up discharge roller 16 into the face up discharge tray 17, while the other being the system to discharge sheet S according to the order of the page in face down posture i.e., with the image plane facing down, wherein the sheet is turned over after being guided upward from the said face up discharge roller 16, via the sheet delivery direction change-over system such as flapper and sheet guide etc. and discharged through the face down discharge roller 18 into the face down discharge tray 19.
Maintenance of the laser printer, i.e., prevention of jamming, exchange of process cartridge 3 etc. is executed as illustrated by two dotted lines in FIG. 1 by turning the upper part 2a of the main body 2 of the apparatus upward around the fulcrum shaft P as against the lower part 2b of the main body 2, thus opening the inside of the apparatus and introducing the hand from the direction of arrow A.
In the case of the conventional double face copying machine as illustrated in FIG. 2, the image is transcribed by photosensitive drum 4 and fixed by fixing apparatus 15 on the 1st face of the sheet delivered from the sheet feeding cassette 10 and the sheet is delivered in S-letter shape by the rollers 16, 51 and 52. Then after inverting the sheet S at a pass 53, timing is adjusted by carrying rollers 54 and 55 at regist roller 12 and the image is formed on the 2nd face of the sheet S by photosensitive drum 4.
In the case of the rolled sheet discharge section of the conventional facsimile, rolled sheet 57 on which the image is formed by image forming section 56 is further carried forward and cut by the cutter 58. Thus cut sheet 57 droops down at the discharge outlet and the front end of the sheet 57 enters into the inverting hole 59 (FIG. 3A). Due to the bend of the sheet, loop 57a is formed (FIG. 3B), the roll is cut at the specified length (FIG. 3C) and discharged on the face down discharge tray 17 to be piled up. (FIG. 3D)
With the conventional case as illustrated in FIG. 1, it was necessary to have two kinds of discharge systems i.e., a face up system and face down system and consequently it has the following drawbacks:
(i) Since the apparatus has two discharge trays 17 and 19, it is necessary to have two kinds of discharge rollers, namely, face up discharge roller 16 and face down discharge roller 18 and besides, discharge trays must be set at two places, namely face up tray 17 at one place and face down tray 19 at another place. PA1 (ii) Since the discharging point differs between face up discharge and face down discharge, operability of the system is inferior. PA1 (iii) Sheet carrying route of the face down discharge is long and thus there is the higher probability of jamming and it also causes cost increase of the motor due to the increase of carrying torque and cost increased use due to the increase of guide plates. PA1 (iv) Because of the presence of face down carrying route (part surrounded by one point chain in FIG. 1), it is impossible to make the body compact and reduce the area occupied by the apparatus.
The conventional apparatus as illustrated in FIG. 2 has such drawback that an extremely large space in S-letter shape is required at the part where sheet S turns over and thus it is difficult to make the equipment compact.
The conventional apparatus as illustrated in FIG. 3 has such drawback that the system is effective for the rolled sheet 57 that is not so hard to bend but with a sheet having high hardness to bend such as cut sheet S, the front end of the sheet S does not enter into the inverting hole, and sufficient inverting performance is not obtained.